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From: Michal Hocko <mhocko@kernel.org>
To: Vlastimil Babka <vbabka@suse.cz>
Cc: Srikar Dronamraju <srikar@linux.vnet.ibm.com>,
	Sachin Sant <sachinp@linux.vnet.ibm.com>,
	Linus Torvalds <torvalds@linux-foundation.org>,
	LKML <linux-kernel@vger.kernel.org>,
	linux-mm@kvack.org, Mel Gorman <mgorman@suse.de>,
	"Kirill A. Shutemov" <kirill@shutemov.name>,
	Andrew Morton <akpm@linux-foundation.org>,
	linuxppc-dev@lists.ozlabs.org, Christopher Lameter <cl@linux.com>,
	Joonsoo Kim <iamjoonsoo.kim@lge.com>,
	Kirill Tkhai <ktkhai@virtuozzo.com>
Subject: Re: [PATCH 1/3] powerpc/numa: Set numa_node for all possible cpus
Date: Tue, 17 Mar 2020 15:01:22 +0100
Message-ID: <20200317140122.GQ26018@dhcp22.suse.cz> (raw)
In-Reply-To: <65b99db6-3bdf-6caa-74e5-6d6b681f16b5@suse.cz>

On Tue 17-03-20 14:44:45, Vlastimil Babka wrote:
> On 3/16/20 10:06 AM, Michal Hocko wrote:
> > On Thu 12-03-20 17:41:58, Vlastimil Babka wrote:
> > [...]
> >> with nid present in:
> >> N_POSSIBLE - pgdat might not exist, node_to_mem_node() must return some online
> > 
> > I would rather have a dummy pgdat for those. Have a look at 
> > $ git grep "NODE_DATA.*->" | wc -l
> > 63
> > 
> > Who knows how many else we have there. I haven't looked more closely.
> > Besides that what is a real reason to not have pgdat ther and force all
> > users of a $random node from those that the platform considers possible
> > for special casing? Is that a memory overhead? Is that really a thing?
> 
> I guess we can ignore memory overhead. I guess there only might be some concern
> that for nodes that are initially offline, we will allocate the pgdat on a
> different node, and after they are online, it will stay on a different node with
> more access latency from local cpus. If we only allocate for online nodes, it
> can always be local? But I guess it doesn't matter that much.

This is not the case even now because of chicke&egg. You need a memory
to allocate from and that memory has to be managed somewhere per node
(pgdat). Keep in mind we do not have the bootmem allocator for the
hotplug. Have a look at hotadd_new_pgdat and when it is called. There
are some attempts to allocate memmap from the hotpluged memory but I am
not sure we can do the whole thing without pgdat in place. If we can
then can come up with some replace the pgdat magic. But still I am not
even sure this is something we really have to optimize for.
-- 
Michal Hocko
SUSE Labs

  reply index

Thread overview: 24+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2020-03-11 11:02 [PATCH 0/3] Offline memoryless cpuless node 0 Srikar Dronamraju
2020-03-11 11:02 ` [PATCH 1/3] powerpc/numa: Set numa_node for all possible cpus Srikar Dronamraju
2020-03-11 11:57   ` Michal Hocko
2020-03-12  5:27     ` Srikar Dronamraju
2020-03-12  8:23       ` Sachin Sant
2020-03-12  9:30         ` Vlastimil Babka
2020-03-12 13:14           ` Srikar Dronamraju
2020-03-12 13:51             ` Vlastimil Babka
2020-03-12 16:13               ` Srikar Dronamraju
2020-03-12 16:41                 ` Vlastimil Babka
2020-03-13  9:47                   ` Joonsoo Kim
2020-03-13 11:04                     ` Srikar Dronamraju
2020-03-13 11:38                       ` Vlastimil Babka
2020-03-16  8:15                         ` Joonsoo Kim
2020-03-13 11:22                   ` Srikar Dronamraju
2020-03-16  9:06                   ` Michal Hocko
2020-03-17 13:44                     ` Vlastimil Babka
2020-03-17 14:01                       ` Michal Hocko [this message]
2020-03-11 11:02 ` [PATCH 2/3] powerpc/numa: Prefer node id queried from vphn Srikar Dronamraju
2020-03-11 11:02 ` [PATCH 3/3] mm/page_alloc: Keep memoryless cpuless node 0 offline Srikar Dronamraju
2020-03-15 14:20   ` Christopher Lameter
2020-03-16  8:54     ` Michal Hocko
2020-03-18  7:50       ` Srikar Dronamraju
2020-03-18 18:57       ` Christopher Lameter

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